According to your words and screenshots, Fruiti, Chir4k reclassed to security just to revenge you, because you killed him as a cop near the security spawn. Of course, that's not what the security class was made for.
On the other hand, I can't tell much without a video. Did you attack him first, forcing him to defend? Securities also have a right to defend themselves.
General reminder for everyone: the duty of the security class is to protect the president. You shouldn't pick this class if you seek to achieve anything else, e.g. to avenge your death.
Chir4k will be also reminded about it.
I am about to lock this, but if you have a video or any other solid proof, please, share it.